1. Field of the Invention
The present invention relates to a method for packaging a zeolite adsorbent. More particularly, it relates to a method for properly packaging, storing and transporting a zeolite adsorbent while suppressing its deterioration. The zeolite adsorbent is useful for separating and recovering oxygen gas, nitrogen gas, carbon dioxide, hydrogen gas or carbon monoxide by separating a gas mixture by a method represented e.g. by a pressure swing adsorption method. Further, the present invention relates to a method for properly filling an adsorption tower with a zeolite adsorbent by means of the packaged zeolite adsorbent.
2. Discussion of the Related Art
A zeolite adsorbent is used usually in a state having moisture removed (activated state). Water shows the highest affinity to such a zeolite adsorbent, and when the zeolite adsorbent in an activated state is in contact with air, it readily adsorbs moisture in the air, and consequently, adsorption sites will be occupied by water molecules, and adsorption of gas molecules will thereby be hindered, thus leading to deterioration of adsorption performance of the zeolite adsorbent.
Therefore, when a zeolite adsorbent in an activated state is to be stored or shipped as a product, it is packaged and then is stored or shipped as a packaged product, so that the zeolite adsorbent will not adsorb moisture present in air.
A zeolite adsorbent product is usually shipped as packaged in a package such as a drum or a supersack (flexible container). If the package is a drum, the product can be packaged in an optional amount within a range of from a few liters to 200 liters depending upon the request by a customer, and it is possible to shield it completely from air by clamping a cover with e.g. a bolt by means of a jig, whereby once it is packaged, substantially no moisture absorption will take place unless the cover of the drum will be opened.
Thus, the packaging method by means of a drum is a method whereby absorption of moisture in air is minimum, and it is utilized as a packaging method for a zeolite adsorbent which is especially desired not to absorb moisture. However, except for a specially designed one, the packaging capacity of a drum is usually at a level of 200 l (about 120 kg when the bulk density of the zeolite adsorbent is 0.6 kg/l) at the maximum, and thus, the drum is not suitable for shipping in a large scale at a level of a few tens tons. For example, for shipment of 50 tons of a zeolite adsorbent, a large number of drums, i.e. at least 400 drums of 200 l capacity, will be required. As the number of drums is large, it takes time for the operation of filling an adsorption tower with the zeolite adsorbent from the drums, whereby substantial moisture will be absorbed until filling of the adsorption tower with the adsorbent has been completed.
When such a large amount of the adsorbent is to be shipped, stored or transported, it is common to employ a supersack (flexible container) having a packaging capacity larger than a drum. The packaging capacity of a supersack is usually from 100 kg to 1 ton, and the supersack is capable of packaging a larger amount of the zeolite adsorbent than a drum. The supersack is composed of an outer bag and an inner bag, and the zeolite adsorbent is put and packaged in the inner bag. As the inner bag, a polyethylene bag is commonly employed for such a reason that the price is low and the handling is relatively simple. However, polyethylene has moisture permeability, and it has been difficult to completely suppress moisture permeability through the material of the inner bag, although an attempt has been made to suppress moisture permeability through the material of the inner bag by a method of making the inner bag to have a double layer structure for packaging the adsorbent.
Further, when the package is a supersack, the inlet portion of the inner bag for the adsorbent is usually tied first by a string for sealing, but is not completely sealed. Accordingly, the open air will penetrate into the inner bag through a clearance slightly present at the sealed portion, whereupon the zeolite adsorbent will absorb the moisture. To prevent the moisture absorption from the sealed portion, sealing may be carried out at two or more positions. Even in such a state, complete airtight sealing is difficult, and moisture will still penetrate into the inner bag. Further, the zeolite adsorbent has a nature to repeat adsorption and desorption of air along with an increase or decrease of the temperature. Accordingly, if a clearance exists at a sealed portion, the open air will be sucked in due to the temperature difference between day time and night time, whereupon the zeolite adsorbent will absorb moisture. On the other hand, inversely, due to an increase of the temperature, the zeolite adsorbent may desorb the adsorbed gas. In such a case, if the packaging bag is completely sealed, the desorption gas will not be discharged out of the packaging bag, and the inner pressure of the bag will increase, and the bag may break, so that the packaged zeolite adsorbent will be in contact with the open air and will be deteriorated by absorption of moisture.
Further, when the zeolite adsorbent is packaged, the product transporting line will be shielded from the open air and maintained to be in a state where the dew point is low, until the product has been packaged, so that moisture absorption will not take place during the transportation through this transporting line until the zeolite adsorbent has been packaged. However, even if a due care is taken to avoid moisture absorption in the product transporting line until the product has been packaged, it is extremely difficult to avoid moisture absorption from the sealed portion of the inner bag or through the material of the inner bag of the supersack during the storage of the product in a warehouse or during the transportation by a ship over a long period of time.
JP-A-10-181792 proposes to provide at least one vent on the side of a supersack for packaging a powder, and a water- and moisture-proofing cloth is stitched on the front side of this vent, and the stitching is done along both side portions and the upper portion only, and the lower portion is left unstitched so that the inner air of the supersack may flow out through the unstitched portion. However, even if such a packaging bag is used for packaging a zeolite adsorbent, the zeolite adsorbent has a nature to repeat adsorption and desorption of a gas due to a change of the open air temperature and has a high adsorption affinity to the gas, and accordingly, even through a slight clearance, the open air is likely to flow into the bag and moisture adsorption will take place. Although, JP-A-10-181792 proposes to provide a water- and moisture-proofing cloth, if a clearance is present at any portion of the bag, the open air will flow in therethrough, and the packaged zeolite adsorbent will be moistened. Even if the four sides of the water- and moisture-proofing cloth were stitched, the amount of the open air passing through due to the adsorption and desorption of the zeolite adsorbent would be large, and the water- and moisture-proofing cloth would soon be saturated by moisture, whereby storage or transportation for a long period of time would be difficult. Further, with respect to sealing of the inlet for the powder, no moisture-proofing means is provided, and it is unavoidable that the zeolite adsorbent will absorb moisture penetrating from the clearance of this sealing portion.
Further, in JP-A-11-59782, a packaging material for transportation excellent in air tightness is employed, and sealing is done by heat sealing. The heat sealing is a sealing method to provide high air tightness, but the heat sealing operation is difficult when a large size supersack is to be sealed. Further, in packaging of a zeolite adsorbent having a nature to repeat adsorption and desorption of a gas, if the packaging bag is completely sealed, when a large amount of gas is desorbed from the zeolite adsorbent, the inner pressure of the packaging bag will increase, and the packaging bag may break. Accordingly, ventilation of the gas will be required.
As described above, for packaging, storing or transporting a zeolite adsorbent by a conventional packaging bag or packaging method, it has been desired to develop a method whereby the operation efficiency can be improved while avoiding deterioration of the quality of the zeolite adsorbent packaged.
The zeolite adsorbent has extremely high affinity to water as compared with the affinity to other gas molecules, and if it absorbs moisture in air before it is used as an adsorbent, its adsorbing performance will substantially decrease, and it will not be able to provide an adequate adsorbing performance. Accordingly, if the zeolite adsorbent is moistened during transportation or storage until shipment after the production thereof, the performance as an adsorbent will deteriorate. Accordingly, it has been desired to avoid moisture adsorption as far as possible. Further, it is necessary to avoid breakage of the packaging bag even if a gas is desorbed from the zeolite adsorbent due to a change of the open air temperature during the storage or transportation. Especially when the production, packaging, storage or transportation is carried out in a large scale as an industrial scale, it is necessary to provide a corresponding precautional measure for packaging, storage and transportation. Further, it is necessary to fill an adsorption tower with a zeolite adsorbent simply and in a short period of time, when the packaged zeolite adsorbent is to be practically used.
Under these circumstances, it is an object of the present invention to provide a packaging method whereby the zeolite adsorbent can be packaged without substantial deterioration as a product, and it will not be moistened during the storage or transportation.
Further, it is another object of the present invention to provide a filling method whereby the zeolite adsorbent thus packaged can be packed into an adsorption tower without deterioration.
The present inventors have conducted extensive studies on the material of a packaging bag which can be used as an inner bag of a supersack, and a packaging method, and further on a method for filling an adsorption tower with a zeolite adsorbent by means of the packaged zeolite adsorbent. As a result, we have found that moisture absorption of a zeolite adsorbent as a product can be prevented by a method for packaging a zeolite adsorbent, which comprises introducing the zeolite adsorbent into a packaging bag having an opening and comprising at least two layers including a metal layer, through said opening, sealing the bag above the introduced zeolite adsorbent, then introducing a dehydrating agent thereon, and sealing the bag above the introduced dehydrating agent, particularly that it is possible to certainly prevent penetration of moisture from the open air by the method wherein at the time of sealing the bag above the introduced dehydrating agent, the packaging bag is folded back and sealed at two or more positions, and further that it is possible to prevent moisture absorption during the period until the zeolite adsorbent is packaged, by the method wherein the packaging is carried out in an atmosphere of dehumidified air having a dew point of not higher than xe2x88x9230xc2x0 C. Further, the present inventors have found it possible to fill an adsorption tower simply and in a short period of time by a method which comprises moving a zeolite adsorbent packaged by the above packaging method to a position above the adsorption tower to be packed, and then opening a lower portion of the packaging bag to let the zeolite adsorbent drop into the adsorption tower to be packed. The present invention has been accomplished on the basis of these discoveries.